Materials with good stretchability and elasticity are used to manufacture a variety of disposable articles in addition to durable articles including incontinence pads, disposable diapers, training pants, clothing, undergarments, sports apparel, automotive trim, weather-stripping, gaskets, and furniture upholstery. For clothing, stretchability and elasticity are performance attributes that allow the materials to provide a closely conforming fit to the body of the wearer.
Propylene-based polymers having good elastic properties are known and have been used for stretchable clothing. See, for example, U.S. Pat. Nos. 6,525,157 and 6,342,565.
U.S. Pat. Nos. 8,178,031 and 7,867,433 disclose methods for making crosslinked elastomeric compositions and articles made from the elastomeric compositions. The elastomeric composition comprising at least one propylene-based polymer is blended with at least one component selected from multifunctional acrylates, multifunctional methacrylates, functionalized polybutadiene resins, functionalized cyanurate, and allyl isocyanurate; and blended with at least one component selected from hindered phenols, phosphites, and hindered amines. The propylene-based polymer may include propylene derived units and one or more dienes, and have a triad tacticity of from 50% to 99% and a heat of fusion of less than 80 J/g. The blended composition may then be extruded and crosslinked. The extruded polymer may be crosslinked using electron beam radiation having an e-beam dose of 100 KGy or less. The crosslinked polymers are particularly useful for making fibers and films.
PCT Publication WO 2011/041230 discloses crosslinked polyolefin blends, methods for their production, and articles made of the same. The polyolefin blends comprise a first polymer formed in a first reactor and a second polymer formed in a second reactor. The first and second polymers, as well as the resulting blend, may comprise units derived from propylene, ethylene, and a diene. The blended composition may then be compounded with one or more co-agents, antioxidants, and/or other additives and crosslinked, preferably by exposure to energetic photons. The crosslinked polymers are particularly useful for making fibers, films, and nonwovens.
U.S. Patent Application Publication No. 2012/0220682 discloses a method for making a crosslinked elastomeric article. The method comprises (a) forming an elastomeric composition comprising at least one propylene-based polymer and at least one component selected from hindered phenols, phosphites, and hindered amines, (b) adding at least one co-agent selected from multifunctional acrylates, multifunctional methacrylates, functionalized polybutadiene resins, functionalized cyanurate, and allyl isocyanurate; (c) extruding the resulting elastomeric composition with an extruder; and (d) crosslinking the extruded elastomeric composition using electron beam radiation having an e-beam dose of about 200 kGy or less, wherein the co-agent is added to the extruder downstream of the elastomeric composition.
However, it has been found that when the liquid co-agent, such as a multifunctional acrylate, is injected into the extruder using a continuous feeder that utilizes a conventional positive displacement centrifugal or gear pump, such as those feeders available from Zenith, gels may be formed on the shaft of the pump, which may lead to seizing of the shaft or even breaking of the shaft. This can lead to a failure to continuously and consistently feed the co-agent to the extruder, which can lead to forming elastomeric compositions that have inconsistent properties. Not intending to be bound by theory, it is believed that the gel formation occurs because the high shear within the operation of the pump induces self-polymerization of the co-agent on the shaft. As the co-agent has an adhesive nature to metals, as gels are formed they bond to the shaft which leads to the shaft bonding to the pump body, resulting in reduced clearance between the shaft and the pump body.
Therefore, there is a need for an improved method of making such elastomeric compositions, and improved methods for making an article comprising such composition.